A species of coin fraud has arisen in which a fraudulent user accesses the coin return hopper of a coin telephone instrument and stuffs the hopper with a wad of material which interferes with the normal function of the instrument to return deposited coins. Fraudulent users do so in the expectation that subsequent legitimate users will be prevented from retrieving coins that should be returned to them so that coins will accumulate behind the blocking wad. Legitimate customers may thus falsely be led to believe that the telephone company inadvertently or deliberately neglected to return their coins. After a while, the fraudulent user returns to the vandalized telephone instrument, removes the blockage and retrieves the fraudulently stored coins. Apparently, two different techniques have been employed by fraudulent users. In one, a balloon is inflated inside the coin return hopper after the coin return door has closed. In the other, a wad of stuffing material is inserted into the coin return hopper and a tool used to force the coin return door to close. While devices have apparently been devised to inhibit coin return hopper stuffing, it appears that such devices tend to jam the coin return chute when a large number of coins are required to be returned to a legitimate user, thereby necessitating that a technician be dispatched by the telephone company to clear the coin path. It would be advantageous to overcome the difficulties of prior art methods of attempting to prevent coin return hopper stuffing.